This invention generally relates to load bearing members for use in elevator systems. More particularly, this invention relates to an elevator belt assembly having a prestretched polymer cords encased in a polyurethane material.
Elevator systems typically include a cab and counterweight that move within a hoistway to transport passengers or cargo to different landings within a building, for example. A load bearing member, such as roping or a belt typically moves over a set of sheaves and supports the load of the cab and counterweight. There are a variety of types of load bearing members used in elevator systems.
The traditional load bearing member has been a steel rope. While this arrangement has proven useful, those skilled in the art are always striving to make improvements. Lighter weight and greater strength are two example load bearing assembly characteristics that are highly desirable. Larger buildings, for example require elevators that travel greater distances, which increases the required length of the load bearing assembly. Lighter weight alternatives would improve the economies associated with elevator systems in such buildings.
While some alternative belt arrangements using lighter weight materials have been proposed, there is a need to satisfy typical safety codes and passenger ride quality standards. Typical codes require belts to meet selected strength criteria, and ride quality requires a minimum amount of stretch. If alternative materials were used, the design issues associated with meeting strength and stretch requirements potentially becomes more complex. Lighter weight materials may be more susceptible to stretch and have different breaking strengths depending on the material composition.
This invention provides a solution to making a load bearing assembly, which has polymer material cords instead of steel, that is able to satisfy strength and stretch requirements.